Optically healable supramolecular polymers.

Polymers with the ability to repair themselves after sustaining damage could extend the lifetimes of materials used in many applications. Most approaches to healable materials require heating the damaged area. Here we present metallosupramolecular polymers that can be mended through exposure to light. They consist of telechelic, rubbery, low-molecular-mass polymers with ligand end groups that are non-covalently linked through metal-ion binding. On exposure to ultraviolet light, the metal-ligand motifs are electronically excited and the absorbed energy is converted into heat. This causes temporary disengagement of the metal-ligand motifs and a concomitant reversible decrease in the polymers' molecular mass and viscosity, thereby allowing quick and efficient defect healing. Light can be applied locally to a damage site, so objects can in principle be healed under load. We anticipate that this approach to healable materials, based on supramolecular polymers and a light-heat conversion step, can be applied to a wide range of supramolecular materials that use different chemistries.

Thermo-, photo-, and chemo-responsive shape-memory properties from photo-cross-linked metallo-supramolecular polymers.

Films exhibiting multiresponsive shape-memory properties have been accessed using covalently cross-linked metallo-supramolecular polymers. Low molecular weight poly(butadiene) was end-capped with 4-oxy-2,6-bis(N-methylbenzimidazolyl)pyridine (-OMebip) ligands that upon addition of metal salts spontaneously formed high molecular weight metallo-supramolecular polymers. The addition of a tetra-functional thiol along with a photoinitiator results in mechanically stable films via solution-casting. These films consist of a soft poly(butadiene) phase and a hard metal-ligand phase. Photo-cross-linking of the poly(butadiene) soft phase, via the thiol-ene reaction, upon exposure to relatively low intensity light, allows access to a diverse range of permanent shapes. Investigations into the temporary shape fixing and recovery of these materials were undertaken to determine the effects of cross-link density and the nature of the metal salts. The key component in fixing and releasing the temporary shape is the metal-ligand hard phase, and as such any stimulus that can disrupt this phase (light, heat, or chemicals) can be used to create the temporary shape and induce its recovery back to the permanent shape.

Directed Self-Assembly of Metallosupramolecular Polymers at the Polymer-Polymer Interface.

Directed self-assembly of a metallosupramolecular polymer is achieved at the interface between two polymer films by simple melt pressing. Blends of a 2,6-bis(N-methylbenzimidazolyl)pyridine (MeBip) side-chain functionalized polystyrene in a polystyrene matrix and Zn(NTf2)2 in a poly(methyl methacrylate) matrix were pressed together above the Tg of the matrix polymers resulting in diffusion of the components and subsequent self-assembly of the metallosupramolecular polymer at the polymer-polymer interface. The formation of the metallosupramolecular polymer was monitored by spectroscopy and microscopy and it was found that the interfacial self-assembly occurs at the processing temperatures (ca. 210 °C) within 5 min. It was further shown that this materials system resulted in robust films that exhibited a new emergent property, namely, phosphorescence, which is not exhibited by any of the individual components nor the metallosupramolecular polymer itself.